The "k" of kHz (4)
I believe the answer is:
kilo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the k of khz</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for kilo that I've seen before include "Metric unit of weight" , "Unit of weight (abbr)" , "Unit of mass" , "2.2 lbs" , "more than two pounds" .)